I've owned this for about 18 months, and to be honest I never understood what all the fuss is about. It's certainly a well built unit with high quality parts, but the design is antiquated and doesn't produce a very sharp Q. I recently sent my unit to an engineering friend of mine with more that 40 years experience in the field of AM SW DX'ing to see if he could

a) sharpen the Q
b) bring down the tuning to 150 khz

His quotes pretty much sum up my thoughts, "I noted, right away that they elected to use parallel tuning for the preselector function. I see no reason for any engineer to do that kind of thing - especially with everything we have learned in the past 10 or 15 years about signal preconditioning. My guess is because it makes mounting the tuning capacitor very easy in production, being bolted to the chassis and front panel. Otherwise it would have to be electrically insulated from ground. In all the preselectors I build, this is one of the inconveniences I have to deal with...isolating the tuning cap...but none the less, a requirement. Unfortunately with the parallel configuration, it is impossible to obtain a high Q. For the life of me, I can't understand why an engineer would put all those 'first class' components into a product and then not design it for optimal performance."

He put into words everything I've been thinking for the last 18 months. If I didn't already own it, I'd be in no rush to go out and purchase one given its high $$$ price tag.

Both the MFJ 956 and PALSTAR MW-550P are pre-selectors that add additional tuned circuits before the front-end of a receiver to reduce spurious signals appearing where they shouldn’t be on the dial. They should be thought of as filters, rather than devises to increase signal strength, although sometimes, under the right combination of things, they do increase signal strength.

My first pre-selector was the MFJ-956, which costs about $50. Without it, dx’ing LW, MW or SW frequencies would have been about impossible at my previous home, since it was 7 blocks away from a 5KW MW transmitter that was directional in my direction after sunset. Using my finest two radios, a PALSTAR R-30C and a KIWA-modified ICOM R-75, there were a few places on the MW band that could not be dx’d without the 956, and there were numerous spurious signals between 1.6 and 5 MC. The 956 cut down the number of spurious signals between 1.6 and 5 MC to just a hand full, and there were no open frequencies on MW or LW that I could not dx successfully. With portable sets, like my Super Sangean 909 from RADIOLABS, I could dx most frequencies, but there were a few spots on the dial when overload could not be controlled without reducing the RF gain down to where very weak signals did not come in.
When I had sufficient funds to purchase the MW-550P, I was anxious to test the two side-by-side for an apples-to-apples comparison. The only band that is common between the MFJ-956 and the PALSTAR MW-550P is the MW band.

COVERAGE DIFFERENCES

The MFJ-956 pre-selects LW-MW-SW frequencies from 150KC to 30MC in several bands. No preamplifier. The MFJ-956 has proven to cut the number of spurious responses between 1.6 and 5MC from powerful near-by MW stations dramatically on all my radios. It has also proved it’s ability to reduce or eliminate spurious BCB signals on LW, although some signal attenuation is noticed.

The MW-550P pre-selects only MW frequencies up to about 2MC.

PASSIVE VERSUS ACTIVE

The MFJ-956 is passive, which means no internal amplification.

The PALSTAR MW-550P has a high quality pre-amp that works for all frequencies up to 30 MC. When in MW mode, the PALSTAR unit amplifies only the tuned MW frequency. On shortwave, the pre-amplifier proved to be very effective on weak signals without adding additional spurious signals.

FUNTIONAL DIFFERENCES

The MFJ 956 will only pre-select.

The PALSTAR MW-550P pre-selects, but it adds the capability of being an “antenna matching” unit, which makes sure that the resistance from the antenna is the same resistance as the receiver, thus maximizing signal transfer from the antenna to the radio. This feature is variable, assuring a good match under virtually all conditions. Compare it to how a 9:1 balun works to maximize signal transfer from a high impedance long wire antenna to a low 50 ohm impedance antenna input on the typical table-top receiver. Since the matching is variable, an exact match can be achieved between virtually any antenna, regardless of the type, and any receiver with a low-impedance input.

WHAT NEITHER UNTIL WILL DO

Neither unit is a true antenna TUNER. If I understand correctly, a true antenna tuner will adjust the electrical length of a random wire antenna to “appear” to the radio receiver to be exactly the wave length of the signal being received. An actual antenna tuner might be expected to provide some significant signal gain, but since this concept of antenna resonance is more important for transmitting than for receiving, antenna tuners are only commercially available for the amateur radio frequencies, so far as I know. A true antenna tuner must have both variable inductance and capacitance adjustments. The inductance is often adjusted with a rolling inductor coil mechanism. Both the MFJ and PALSTAR units compared in this review will only vary the capacitance on the band being tuned.

PERFORMANCE COMPARISONS FOR MEDIUM-WAVE DX’ING
All tests done May 2006 around noon on weakest available MW signals.

SIGNAL LOSS COMPARISONS

Use of the 956 almost always resulted in several decibels of signal strength loss. The MW-550P never caused signal strength loss, seeming to have negligible insertion loss, and the built-in pre-amp on MW amplifies only the pre-selected frequency, so there was never a time when signal strength was less. The use of the MW-550P on weak signals made station ID from the announcer’s voice easier in many situations, compared to the bypass setting. (This comparison only being possible, of course, on weak signals that could be received without interference from spurious signals in the BYPASS mode.)

SELECTIVITY COMPARISONS

Without test equipment, my observations are subjective as to extent of difference but objective as far as the general result. The MW-550P appears to offer several times better signal rejection for stations close to each other on the dial. This means that a station even 10 or 20 KC away from a powerful local station bleeds over significantly less on the MW-550P than the MFJ-956. However, for $50, the MFJ unit provides good results in this area for the price. Even on the smooth veneer tuning dial of the MW-550P, it takes a very definite re-adjustment to peak that signal. This difference is probably due to the massive inductor used on the PALSTAR which apparently has a very high Q rating.

From my location here in South Western Ohio, the weakest day-time MW signals come from WSM in Nashville, TN (650KC), KDKA in Pittsburg, PA (1020KC), and Boston, MA (1030KC) at this time of year (spring). On the particular day and hour I was doing my comparison testing, the signal from WSM was especially weaker than normal, due to varying day-time ionospheric conditions between here and Nashville, which made for ideal testing conditions for a device like this.

DX’ing KDKA and WBZ present a combination of problems. The MW transmitter seven blocks from my home may be over-modulating. Between 1000KC and 1090KC there is a distorted ‘hash” that is minimal when a human voice is being broadcast by the powerful local, but very bad when music is being broadcast. This interference is so bad without a pre-selector that 1020KC and 1030KC can not be received on any of my radios. With the MFJ-956, both stations come in weakly because the splatter from the local station is significantly reduced. However, with the PALSTAR MW-550P, the hash , although still present, is only about one third as obtrusive, the signal strength is greater, and the audio of both weak signals is more listenable.

PROBLEMS

The MFJ-956 can not pre-select my 175’ random wire antenna properly between 530KC and 660KC to tune a signal peak. The lowest setting on the tuning capacitor is not low enough to tune below 650KC. You can put the range selector on LW and tune to the upper part of the LW band by the tuning capacitor on the pre-selector, but this procedure results in a crippling reduction is signal strength, even though you can peak the signal at the 650KC frequency. The tuning capacitor does not appear to have enough range when used with longer antennas.

The PALSTAR MW-550 exhibited no such problems and tuned clear down to 530KC with the 175’ antenna with a definite signal peak on the tuning capacitor.

USE WITH PORTABLE SETS

I reasoned to myself that the worse the radio, the better my ability to test the effectiveness of the pre-selectors. For this purpose, I used my RADIOLABS Super 909. My Super 909 is a Radio Shack DX-398 clone that I sent to RADIOLABS for the Super 909 modifications.

Portables usually have poorly designed front-ends, and this radio is no exception. Keep in mind that the testing conditions are extreme. If you lived far away from any MW stations, you might not notice very much difference between a good portable and a good table-top receiver. However, my receiving station was 7 blocks from a 5KW station and I was using a 175 foot random wire antenna through a 9:1 balun.

My best signal transfer for MW was with a BCB loop antenna connected to the output of the pre-selectors to a BCB loop antenna taken out of an old AM-FM tuner and which was placed over the ferrite bar MW antenna in the Super 909. This arrangement allowed for adjusting the degree of signal transferred to the radio by varying the degree of inductive coupling for optimal results. As far as I could tell, comparing the quality and decipherability of the audio on very weak signals, the Super 909 with the 15db attenuator and inductive coupling was just as effective as either of my table-tops hooked directly up to the low impedance antenna input without the 15db attenuator. Interestingly, I found that the portables worked best without a ground connection, but the table tops worked best with the ground connection. Since S meter readings can not be compared between any two different receivers, I am not using s-meter readings to justify this conclusion. If the 15db attenuator on the MW-550P was not used with the 909 via inductive coupling, front-end over-load occurred in many situations.

With the MFJ-956, there were some cases where I could not prevent signal over-load to the 909 unless I reduced the inductive coupling down to where over-all reception was reduced to below that of the table-tops. However, with the PALSTAR MW-550P, I was able to use the 909 at any frequency on the BCB with proper adjustment of the controls and inductive coupling. Again, while it was necessary to use the 15db attenuator to use all available frequencies without spurious responses on top of them, it seemed that with the 15db signal attenuator on the MW-550P and the inductive coupling positioned for maximum signal transfer to the radio‘s ferrite bar antenna, there was no signal loss when compared to a direct connection to the table tops.

Also, in the toughest over-load situations with the Super 909 radio and the MW-550P, adjusting the antenna matching control could clear up even the toughest over-load problem. It was like magic! Nothing else I tried seemed to work in some situations. Reducing the RF gain on the Super 909 didn’t work. Reducing the inductive coupling between the BCB loop antenna and the Super 909 didn’t work without reducing signal strength below that of the table-tops. Then, to my amazement, when I adjusted the antenna matching capacitor on the MW-550P, Presto! The frequency cleared of the spurious signals, and there was the desired weak signal!

When using a radio with a weak front-end, it is necessary to know where to set the pre-selector’s tuning control to achieve reception of a particular frequency. This is because with either pre-selector, tuning the pre-selector from one end to the other of it’s tuning range causes a wide variety of spurious signals to sweep across the desired frequency to which your radio is set, and then disappear. There are far fewer such spurious signals when using the MW-550P sweeping across the frequency to which the radio is set, but even one spurious signal can be mistaken for the actual signal. Knowing which signal is the one at the desired frequency and which ones are spurious over-load products is not easy unless you know your pre-selector dial setting. Of course with a good table-top, like my PALSTAR R-30C or ICOM R-75, there are no spurious signals whipping by your desired tuned frequency, so all you have to do is adjust the pre-selector for maximum noise or signal level. With either a table top or portable and the MW-550P, however, the end result was the same. Ultimately, there was no open BCB frequency I could not tune, despite being 7 blocks from a local station and using a 175’ random wire antenna!

The MW-550P taught me some amazing things about portables versus table-tops. It seemed that the sensitivity of a good portable like the Super 909 is about the same as a table-top, but there is an unbelievable difference in these classes of radios when it comes to their ability to handle strong signals. My testing has brought me to an almost unthinkable conclusion. For MW dx’ing in a strong signal environment, I would choose the MW-550P and a good portable set combination over a good table-top receiver and no MW-550P. This is because the combination would allow for dx’ing all available frequencies, but the table top connected directly to the antenna would not.

CONSTRUCTION QUALITY

The PALSTAR product is much more expensive, but it is designed the operate under any possible antenna-receiver combination, and it is built like the proverbial “tank.” I am on my second MFJ-956, the first unit having quit after a couple of years of steady use. While the MW-550P is more than five times as expensive as the MFJ-956, it gives you eight times better value for your money when ultimate performance is what is desired.

The main variable capacitor in the MW-550P is huge and features a tuning range that is extremely wide. This is why you can tune from 530KC to about 2MC in one range. The Q coil is very large also and is specially designed and wound to provide sharp tuning selectivity through the highest possible Q.

SUMMARY

As a MW dx’er, I have always dreamed about owning something like the PALSTAR MW-550P, but it did not exist until recently. Now, thanks to the MW-550P, it is possible for a dx’er to live almost right under the transmitter of a local radio station and DX any available frequency. To my knowledge, this has never been possible before. Other users of the MW-550P have reported that it works well with tuned loop antennas like the QUANTUM and KIWA loops. (The MFJ-956 can also probably be used with these antennas, but with somewhat lesser results.)

Thanks to it’s sharp selectivity, the MW-550P is able to attenuate signals just 20-30KC away well enough to dx near-by frequencies that would be impossible to hear, even with a very good table-top radio by itself. It appears to give several db of attenuation just 10KC from the desired frequency-- perhaps just enough under critical conditions, such as trans-continental dx’ing-- to make the difference between hearing the station and not hearing it.

The SWL has always had a few good quality pre-selectors to choose from, both active and passive. For the MW dx’er, however, this was not the case until the PALSTAR MW-550P came along. The MW-550P seems undaunted by long random wire antennas, and it appears to me that it would be able to handle beverage antennas of unlimited length. By contrast, the MFJ 956 could not accommodate an antenna of even 175 feet and still be able to resonate frequencies around 650MC or below. The 956 might work better with antennas around 100 feet long, but antennas this short are not able to provide much improvement over trying to pull in the same signal on a good car radio.

If you DX both long wave and short wave, the MFJ-956 is the only one of the two pre-selectors that can help you fight off spurious images from strong local MW stations. For example, the MFJ unit eliminated almost all spurious MW signals on the long-wave band, even when using the RadioLabs Super 909. Since I am interested in both long-wave and short-wave dx’ing and have lived in the shadow of the tower of a local AM radio station, I own both the MFJ-956 and the PALSTAR MW-550P.

POST SCRIPT

I have recently moved to a location five miles from the nearest MW station in my area with underground utilities. As soon as I am able to install a 250 foot random wire antenna, I plan to do some additional testing and add a review of my additional findings and comparisons.

I bought this preselector as my Drake R8 deals rather poorly with my two local 10KWers on 630 and 720. From 1350 on up, the R8 is a zoo, especially when the ground is damp and local ground conductivity is high. My Hammarlund HQ-180 does not suffer from this problem, nor does my Collins R-390A as both use tuned front ends - the former using the tried and true variable capacitor method, the latter using a superb system of variable inductors. My Ten-Tec RX-321, flawless technobox that it is, also does not have this problem. Only the otherwise lovely Drake R8.

The Palstar MW550P totally "fixes" the Drake R8 and no longer do my locals pop up while MW DXing. Nothing more frustrating than thinging you have some exotic new catch up on 1650 KHz in the X-Band only to hear it ID, "Good Time Oldies, 720 CHTN"!

But wait, there is more! The Palstar also helps to tighten bandwidth on my other receivers, making reception of 710 WOR more possible in the wake of CHTN's splatter or 1314 Norway in the wake of 1320 CKEC's wide band, HiFi splatter.

Peaking a weak signal to resonance with the Palstar actually tames the noise a bit, and the preamp is excellant - very overload proof.

The real proof of how good the Palstar is can be revealed in the fact that it actually enhances weak signal MW DX with the Collins R-390A!

Customer service is tops with Palstar - I had a minor problem, contacted the company and the problem was solved. Kudos to Palstar!

Works great when used with a Quantum QX Pro Loop and Quantum Phaser. Run the loop into antenna "A" of the Phaser. Run your long wire into the MW550P, then run the output of the MW550P into the antenna "B" input of the Phaser. This way, both your loop and your long wire can be tuned with lots of Q, then phased against each other for directionality, phasing out noise, etc. What a combination and there is then no need to use the Q spoil control on the loop!

In Canada, the requirement for code for HF amateur radio was recently dropped. VHF/UHF always was of no interest, but when I recently learned that code was no longer required for 160 to 10 M here, I did the dance of joy, contacted the RAC, ordered study materials, then bought a Kenwood TS-520SE on eBay - I'm awaiting delivery. I'll likely need an antenna tuner - so where do you think I'll buy it - Palstar of course.

By the way, the Palstar MW550P is built like a tank - I opened it up of course!

Built to last!

I will add that the MW-550P is not for the casual MW DXer. But for the MW DXer with just about all the right DX tools, this is a great addition to your MW DX shack!

This is a perfect companion to my AY Technologies K9AY Loops and controller - BCB DX-ing and 160M and 80M reception has never been better for me! I use a Palstar R30 for BCB and SWL-ing, and an Orion for low band DX-ing.

This winter I will also add a couple of Beverages, and I know that the MW550P will handle these as well as it does the K9AY loops.

The only thing I wish is that it had an antenna input switch for 2 antennas, and a switch for 2 receivers. (Like the MFJ-959C - but I'll take the Palstar build quality over the MFJ any day).

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